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mm/khugepaged: collapse_shmem() stop if punched or truncated

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Huge tmpfs testing showed that although collapse_shmem() recognizes a
concurrently truncated or hole-punched page correctly, its handling of
holes was liable to refill an emptied extent.  Add check to stop that.

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1811261522040.2275@eggly.anvils
Fixes: f3f0e1d215 ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: <stable@vger.kernel.org>	[4.8+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2018-11-30 14:10:25 -08:00 committed by Linus Torvalds
parent 006d3ff27e
commit 701270fa19
1 changed files with 11 additions and 0 deletions
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11
mm/khugepaged.c
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@ -1359,6 +1359,17 @@ static void collapse_shmem(struct mm_struct *mm,
VM_BUG_ON(index != xas.xa_index);
if (!page) {
/*
* Stop if extent has been truncated or hole-punched,
* and is now completely empty.
*/
if (index == start) {
if (!xas_next_entry(&xas, end - 1)) {
result = SCAN_TRUNCATED;
break;
}
xas_set(&xas, index);
}
if (!shmem_charge(mapping->host, 1)) {
result = SCAN_FAIL;
break;